Cholesteric liquid crystal displays (ChLCD's) have existed for several decades. ChLCD's are unique because of their “nonvolatile memory” characteristic; once an image is written to a display, the current image will remain indefinitely until a new image is written. ChLCD's can also be viewed in ambient light without back lighting. Both of these characteristics significantly reduce total power consumption when compared to other displays.
On the other hand, ChLCD's have inherently slow refresh rates. In an effort to address slow refresh rates associated with ChLCD's, drive schemes for ChLCD's have evolved significantly and have become very complex. Known drive schemes include bipolar and multi-phase drive schemes. Bipolar drive schemes frequently have insufficient voltage to effectively drive a ChLCD, and the complexity of both bipolar and multi-stage drive schemes results in high costs.
There exists a need for a simple, low cost way to achieve gray scale reflection using unipolar drive signals.